Use model alias

[yujonglee]

https://docs.litellm.ai/docs/completion/model_alias

This can be useful for 2 cases

• llama2: replicate/llama-2-70b-chat:2796ee94...
• gpt-3.5-turbo, gpt-3.5-turbo-16k, ... to single GPT3.5

[yujonglee]

I think it will be more complicated. For GPT 3.5 mapping, #70 will do.

[krrishdholakia]

@yujonglee what would the ideal solution here have been?